1. Field of the Invention
The present invention relates to a focus control device used for recording and playing back of information with respect to an information recording medium, such as magneto-optic disk, an optical disk, or the like. More particularly, the present invention relates to a focus control device to perform focus control with respect to a multi-layer recording medium having a plurality of recording layers.
2. Description of the Related Art
In recent years, various methods have been proposed to increase the storage capacity of magneto-optic disks and the like information recording media. For example, one proposed method of increasing the storage capacity of disk-type recording media is to increase the number of recording layers, thereby increasing the data density of the information recording media.
To perform recording or playback of information with respect to the known disk-type recording media, a converged light beam illuminates the surface of the recording medium. During recording or playback of information, focus control is performed to control the converged light beam such that its focus position is on the recording surface of the recording medium. However, the conventional information recording and playback devices can not perform focus control on each recording layer of a multi-layer recording medium because the conventional recording and playback devices have a recording medium with a single recording layer as the control subject.